Process for improving cloud point of petroleum gas oil by caustic washing thereof from hydrocarbon mixtures



United States Patent 3,259,549 PROCESS FOR IMPROVING CLOUD POINT OF PE- TROLEUM GAS OIL BY CAUSTIC WASHING THEREOF FROM HYDROCAON MIXTURES Charles Vernet and Bernard Maurice Laine, Lavera, France, assignors to The British Petroleum Company Limited, London, England, a British joint-stock corporation No Drawing. Filed Dec. 16, 1963, Ser. No. 330,526 Claims priority, application Great Britain, Dec. 31, 1962, 49,056/ 62 14 Claims. (Cl. 1953) This invention relates to a process for the production of micro-organisms, for example, yeasts. This invention also relates to a process for the removal of straight chain hydrocarbons, wholly or in part, from mixtures of said hydrocarbons with other hydrocarbons.

It is well-known that certain pertoleum fractions, particularly gas oils, contain straight chain hydrocarbons, mainly paraflins which are waxes and which hzwe an adverse etfect upon the pour point of the fraction; that is to say, when these hydrocarbons are removed, wholly or in part, the pour point of the fraction is lowered. Usually the wax is removed by precipitation 'by means of solvents, the wax originally present in the fraction being recovered as such, that is, without conversion to more valuable products.

The petroleum fractions boiling below the gas oils, for example, heavy naphthenes and kerosines also contain straight chain hydrocarbons which are potentially valuable for conversion to other products but hitherto, in general, utilisation of these hydrocarbons has been rendered difficult by the necessity of recovering these hydrocarbons from the petroleum fractions, in which they are contained, before they can be converted to other products.

In a process in which a micro-organism is used for the removal, wholly or in part, of straight chain hydrocarbons from hydrocarbon mixtures it has been found that, in general, the process gives rise to the formation of carbon, hydrogen and oxygen containing lay-products, for example, esters. These by-prod-ucts may remain in the hydrocarbon fraction which is separated from the microorganism and constitute a contaminant. in particular, when the feedstock is a Wax-containing gas oil, the recovered gas oil may have an unacceptably high cloud point by reason of the presence of these by products.

We have found that these by-products may be removed or converted into less detrimental products by caustic washing.

According to the present invention there is provided a process which comprises, in a micro-organism growth stage, cultivating a micro-organism in the presence of a hydrocarbon feedstock consisting of a mixture of straight chain hydrocarbons with other hydrocarbons; in the presence of an aqueous nutrient medium; and in the presence of gas containing free oxygen, thereafter separating the micro-organism from the hydrocarbon residue and subjecting this residue to a caustic wash.

Suitably there is used, as feedstock a hydrocarbon fraction derived from petroleum.

The process of the invention is of particular value for the treatment of petroleum gas oil fractions which contain straight-chain hydrocarbons in the form of waxes, since by the process of the invention, a gas oil of improved pour point is obtained while the waxes are converted to a valuable product.

Usually the straight-chain hydrocarbons will be present in the feedstocks according to the invention as paraffins; however, the straight chain hydrocarbons may be present as olefins; also there may be used a mixture containing straight chain parafiins and olefins.

It is an important feature of this invention that when cultivating yeasts in the presence of the feedstocks herein'before described under conditions favouring the growth of the yeasts at the expense of the straight chain hydrocarbons, the other hydrocarbons, for example isoparaffins, naphthenes and aromatics are not metabolised or, at most, the proportion which is metabolised is very small. Furthermore, unlike conventional chemical processes governed by the law of mass action, the rate of removal of straight chain hydrocarbons is not substantially reduced as the proportion of these hydrocarbons in the overall mixture of hydrocarbons decreases (except, of course, in the very final stages of removal). Thus, when desired, the percentage conversion of straight chain hydrocarbons which is achieved can be maintained at a value approaching without necessitating a very disproportionate expenditure of contact time to achieve small improvements. Furthermore, in the continuous process, this high percentage conversion can be achieved without resorting to the use of a long reaction path.

By the application of this process under conditions which limit the metabolisation of the straight chain hydrocarbons it is possible to operate with the removal of only a desired proportion of these hydrocarbons.

Suitable feedstocks to the process of the invention include kerosine, gas oils and lubricating oils; these feedstocks may be unrefined or may have undergone some refinery treatment, but will usually be required to contain a proportion of straight chain hydrocarbons in order to fulfil the purpose of this invention. Suitably the petrol- .eum fraction will contain 3-45 by weight of straight chain hydrocarbons.

Micro-organisms which are cultivated as herein described may be yeasts, moulds or bacteria.

Preferably when a yeast is employed this is of the family C-ryptococcaceae and particularly of the subafamily Cryptococcoideae; however, if desired there may be used, for example, ascosporogeneous yeasts of the sub-family Saccharomycoideae. Preferred genera of the Cryptococcoideae sub-family are Torulops-is (also known as Torula) and Candida. Preferred strains of yeast are as follows. In particular it is preferred to use the specific stock of indicated Baarn reference numbers; these reference numbers refer to stock held by the Centraal Bureau vor Schi'mmelculture, Baarn, Holland:

Candida lipolytica Candida pulcherrima, CBS 610 Candida utilis Candida utilis, variati major, CBS 841 Candida tropicalis, CBS 2317 T ornlopsz's collisculosa, CBS 133 Hansenula anomala, CBS Oidium lactis Neurospora sitophila Of the above Candida lipolytica is particularly preferred.

If desired, the micro-organism may be a mould. A suitable strain is Penicillium expansum.

If desired, the micro-organism may be a bacterium. Suitably the bacteria are of one of the orders: Pseudomonadales, Eubacteriale-s and Actinomycetales.

\Preferably the bacteria which are employed are of the family Bacillaceae and Pseudomonadaceae. Preferred species are Bacillus megaterium, Bacillus subtilis and Pseudomonas aeruginosa. Other strains which may be employed include:

Bacillus amylebacter Pseudomonas natriegens Arthrobacter sp. Micrococcus sp. Corynebacterium sp.

Patented July 5, 1966 Pseudomonas syringae X antlzomonas begoniae F lavobacterium devorans Acetobacter sp. Actinomyces sp.

Suitable moulds are of the family Aspergillaceae. A suitable genus is Penicillium.

Preferably there is used Penicillium exparzsum. other suitable genus is Aspergillus.

Usually the cultivation is carried out in the presence of an aqueous nutrient medium. If desired, certain solid nutrient media may be employed.

In either case, a gas containing free oxygen must be provided.

Penicillizrm expansum is suitable for cultivation in an aqueous nutrient medium containing hydrocarbons.

Penicillium roqueforti, Penicillz'um notatum, Aspargillus fussigatus and Aspergillus niger, Aspergillus versicolor may be used for cultivation on a solid agent containing hydrocarbons as feedstock.

For, the growth of the micro-organism it will be necessary to provide, in addition to the feedstock, an aqueous nutrient medium and a supply of oxygen, preferably in the form of air.

A typical nutrient medium for the growth of Nocardia, a genus in the Actinomycetales order, has the following composition:

Grams Ammonium sulphate 1 Magnesium sulphate 0.20 Ferrous sulphate, 7H O 0.005 Manganese sulphate, 1H O 0.002 Monopotassiurn phosphate 2 Disodium phosphate 3 Calcium chloride 0.1 Sodium carbonate 0.1

Yeast extract 0.008 Distilled water (to make up to 1000 mls.).

For other bacteria a suitable nutrient medium has the composition:

Monopotassium phosphate, grams 7 Magnesium sulphate, 7H 0, grams 0.2 Sodium chloride, grams 0.1 Ammonium chloride, grams 2.5 Tap water (trace elements), mls. 100

Yeast extract, grams 0.025 (Made up to 1000 mls. with distilled water.)

A suitable nutrient medium for yeasts (and moulds) has the composition:

Grams Diammonium phosphate 2 Potassium chloride 1.15 Magnesium sulphate, 7H O 0.65 Zinc sulphate 0.17 Manganese sulphate, lH O 0.045 Ferrous sulphate, 7H O 0.068 Tap water 200 Yeast extract 0.025

Distilled water (to make up to 1000 mls.).

Micro-organisms, and in particular yeasts, when first cultivated with the use of hydrocarbon fractions as feedstock sometimes grow with difficulty and it is sometimes necessary to use an inoculum of a micro-organism which has previously been adapted for growth on the hydrocarbon fraction which it is intended to use. Furthermore the micro-organism although cultivated in the presence of an aqueous mineral medium containing the appropriate nutrient elements may grow with difficulty, because the hydrocarbon fraction does not contain the growth factors which exist in carbohydrate feedstocks, unless these growth factors are added.

The growth of the micro-organism used is favoured by the addition to the culture medium of a very small proportion of extract of yeast (an industrial product rich in vitamins of group B obtained by the hydrolysis of a yeast) or more generally of vitamins of group B and/or biotin. This quantity is preferably of the order of 25 parts per million with reference to the aqueous fermentation medium. It can be higher or lower according to the conditions chosen for the growth.

The growth of the micro-organism takes place at the expense of the feedstock fraction with the intermediate production of bodies having an acid function, principally fatty acids, in such manner that the pH of the aqueous mineral medium progressively diminishes. If one does not correct it the growth is fairly rapidly arrested and the concentration of the micro-organism in the medium, that is cellular density no longer increases so that there is reached a so-called stationary phase.

Preferably therefore the aqueous nutrient medium is maintained at a desired pH by the step-wise or continuous addition of an aqueous medium of high pH value. Usually, when using moulds or yeasts and in particular when using Candida lipolytica, the pH of the nutrient medium will be maintained in the range 3-6 and preferably in the range 4-5. (Bacteria require a higher pH, usually 6.58.) Suitable alkaline materials for addition to the growth mixture include sodium hydroxide, potassium hydroxide, disodium hydrogen phosphate and ammonia, either free or in aqueous solution.

The optimum temperature of the growth mixture will vary according to the types of micro-organism employed and will usually lie in the range 25-35 C. When using Candida lipolytica the preferred temperature range is 28-32" C.

The take-up of oxygen is essential for the growth of the micro-organism. The oxygen will usually be provided as air. In order to maintain a rapid rate of growth the air, used to provide oxygen, should be present in the form of fine bubbles under the action of stirring. The air may be introduced through a sintered surface. However there may be used the system of intimate aeration known as vortex aeration.

It has been found that by the use of yeast of the strain Candida lipolytica in a process according to the invention in which aeration is effected by vortex aeration, a high growth rate is achieved whereby the generation time lies in the range 2-5 hours and the cell concentration is increased by a factor of up to 12 in two days.

In batch operation, the micro-organism will usually grow initially at a low rate of increase in cellular density. (This period of growth is referred to as the lag phase) Subsequently the rate of growth will increase to a higher rate of growth; the period at the higher rate of growth is referred to as the exponential phase and subsequently again the cellular density will become constant (the stationary phase).

A supply of the micro-organism for starting the next batch will preferably be removed before the termination of the exponential phase.

The growth operation will usually be discontinued before the stationary phase.

At this stage, the micro-organism will usually be separated from the bulk of the aqueous nutrient medium and from the bulk of the unused feedstock fraction.

If desired the micro-organism may be subjected to autolysis before further purification of the product.

According to one method of treating the product the major part of the continuous aqueous phase is first separated; preferably this is carried out by centrifuging or decanting. The separated aqueous phase will usually contain a greater concentration of non-nutritive ions than can be tolerated in the recycle stream and when this is so, only a portion of the recovered aqueous phase can be recycled. Thus it will usually be possible to separate ca. 96% by wt. of the aqueous phase which is present in the product, of which on the same percentage basis, ca. 20% by wt. will be discarded. The recycle stream is supplied with make-up quantities of the necessary nutrients and is returned to the fermenter; if desired the make-up materials may be fed to the fermenter as a separate stream. 1

The process, as applied to the cultivation of a yeast, may incorporate product separation stages as follows. In some cases micro-organisms other than yeasts may be separated in this manner. I

By centrifuging the product from the fermenter three fractions are recovered. These are in order of increasing density:

(i) An oil phase containing yeast cells (ii) An aqueous phase containing traces of oil and yeast, and

(iii) A yeast cream consisting of yeast, having a quantity of oil fixed onto the cells, together with aqueous phase.

After recovery of fraction (ii), fraction (iii) or a blend of fractions (i) and (iii) is mixed with an aqueous solution of a surfactant.

The purpose of this treatment is to separate the oil from the yeast cells; the oil being apparently held to the cells by adsorption.

It may be advantageous to employ an edible surfactant, for example a saccharose ester, which makes it possible to reduce the subsequent washing required to remove from the yeast a surfactant which is not edible.

The emulsion so formed is broken down by centrifuging to obtain three fractions.

(iv) An oil phase (M) An aqueous phase containing surfactant, which phase is recycled for the treatment of fractions (i) and (iii), and

(vi) A yeast cream, consisting of yeast still contaminated by oil together with an aqueous surfactant phase.

In order to reduce as far as possible the consumption of surfactant product, the aqueous washing solution containing it is recycled.

Fraction (vi) may be further treated by alternate washing with surfactant and centrifuging until the oil content of the yeast has reached a desired low value. The yeast cream now consisting of yeast and aqueous surfactant may now be washed with water and again centrifuged. If desired two or more washings may be given to this yeast cream. If desired, one or more of these water washings (but preferably not the last) may make use of salt water (for example, sea water); preferably the final wash is with soft water. With a view to econornising the soft water necessary for the process, the whole of this water coming from the last washing is employed for making up the nutritive medium for the fermentation, where necessary at the stage of washing with the solution of surfactant, and the rest is sent to the salt water used for washing with a view to reducing its salt concentration. Finally the yeast may be dried under conditions suitable for its subsequent use as a foodstuff.

Other steps which may be taken to obtain a purified micro-organism or a product derived therefrom or to improve the process in respect of the production of the unmetabolised hydrocarbon fraction are described in the applications set out hereinafter.

The recovered unmetabolised hydrocarbon with or without an intervening refining stage is subjected to a caustic wash.

Preferred materials for carrying out the caustic wash are aqueous or alcoholic sodium hydroxide and aqueous or alcoholic potassium hydroxide.

If desired, the caustic wash is carried out with a 30- 50% by wt. aqueous solution of the alkali, at a ratio of hydrocarbon to treating medium in the range 1:1 to 1:5 by volume.

If desired the caustic wash may be carried out with a 15-25% by wt. alcoholic alkali metal hydroxide solution at a ratio of hydrocarbon to treating medium in the range 2:1 to 1:2 by volume.

Preferably the stage is carried out with stirring.

The temperature used will usually be in the range 60- C.

Steps which may be taken to obtain a purified microorganism or a product derived therefrom or to improve the process in respect of the production of the unmetabolised hydrocarbon fraction are described in the following applications; the use of any process step or steps therein described in association with the process herein described lies within the scope of the present invention.

The invention is illustrated but not limited with reference to the following examples.

Throughout these examples cellular density is expressed as dry weight of yeast per litre of culture.

Example 1 Gram-s Diammonium phosphate 2 Potassium chloride 1.15 Magnesium sulphate, 7H O 0.65 Zine sulphate 0.17 Manganese sulphate, 1H O 0.045 Ferrous sulphate, 7H O 0.068 Yeast extract 0.025 Tap water 200 Distilled water add. 1000 ml.

20 litres of inoculum from a 24 hr. culture of Candida lipolytica on mixed C -C normal parafiins were then added; cellular density being about 1 gram/ litre.

1.03 litres of heavy gas-oil, that is 15 grams/litre were then added, enough to take the cell density to 2 grams/ litre.

The temperature was kept at 30i1 C., pH 4, aeration and agitation such that the aeration rate was 3 millimoles 0 per litre per hour. Addition of 10 N ammonia was by automatic pH controller.

When the flow of ammonia reached 20 ml. gas-oil was added according to the theoretical needs of the culture, assumed yield 10% of dry yeast produced gas-011 required and assuming a cell division time of 3 hours. This addition took place every hour until 17 litres, that is, 250 grams/litre of gas-oil had been added.

Starting with a cellular density of 2 grams/litre, at 25 hours, at the end of the exponential growth phase, 18 grams/litre were obtained.

Feed gas-oil characteristics:

Density 15 C./4 C. 0.876 Afnor flash point Above Cloud point +20 Pour point +18 N-paraffins, percent wt. 10 Saybolt distillation, C.:

Initial boiling point 221 5% 228 50% 363 95% 402 Final boiling point Above 405 Residual volume percent 1 Loss in volume percent 0 At 25 hours a quantity of culture was withdrawn from the vessel; from this product 300 ml. of non-metabolised gas-oil was obtained by centrifuging at +50 C.

Characteristics of residual gas-oil:

Density at 15 C./4 C. 0.8939 Afnor flash point, C Above 120 Cloud point, C. Pour point, C. 16 N-paraflins, percent wt. 1.8 Saybolt distillation, C.:

Initial boiling point 245 296 50% 365 95% 402 Final boiling point Above 405 Residual volume percent 1 Loss in volume percent 0 300 ml. of the non-metabolised gas-oil and 300 ml. of alcoholic caustic potash, 20% by weight, were introduced into a 100 ml. round-bottomed flask fitted with a reflux condenser, and boiled under reflux for 2 hours. The treated gas-oil was decanted ofl. Its cloud point was lowered from 0 to 16 C.

Example 2 The method described in Example 1 was carried out on gas-oil from a continuous culture of Candida lipolyrim.

3 litres of a continuous culture in a 5 litres fermenter were fed. with 300 ml./hr. of an emulsion containing of heavy gas-oil emulsified in 90% of an aqueous mineral medium as given in Example 1.

Characteristics of the feed gas-oil:

The pH was maintained at 4:01 by the automatic addition of 10 N ammonia. The temperature was held at 30 C.; aeration and agitation were such that the aeration rate was 3 millimoles oxygen per litre per minute.

After a few days the cellular density became stabilised at 10:1 grams/litre and enough culture was then withdrawn to obtain 300 ml. of residual gas-oil by centrifuging at +5 C.

Characteristics of the non-metabolised gas-oil:

Density 0/4 C 0.891 Pour point, C. -8 Cloud point, C. Sulphur, percent wt. 1.86 N-paraflins, percent Wt. 1.6 Afnor flash point, C 147 Saybolt distillation, C.:

Initial boiling point 260 5% 306 50% 364 95% 398 Final boiling point Above 400 Residual volume percent (1) Loss in volume percent This non-metabolised gas-oil was treated as in Example 1. Its cloud point was lowered from +20 to -6 C.

We claim:

1. A process for the removal, at least in part, of waxes from a wax-containing petroleum gas oil which comprises, in a micro-organism growth stage, cultivating a straight chain hydrocarbon consuming-micro-organism in the presence of said wax-containing petroleum gas oil; in the presence of an aqueous nutrient medium, and in the presence of gas containing free oxygen, thereafter separating the micro-organism from the gas oil of reduced content of wax, and subjecting the gas oil to a caustic wash to reduce its cloud point.

2. A process according to claim 1 in which the caustic wash is carried out using potassium hydroxide.

3. A process according to claim 1 in which the caustic wash is carried out using a wash selected from the group consisting of aqueous and alcoholic solutions of an alkali metal hydroxide.

4. A process according to claim 1 in which the caustic wash is carried out using sodium hydroxide.

5. A process according to claim 1 in which the caustic wash is carried out using 3050% by wt. aqueous alkali metal hydroxide at a ratio of hydrocarbon to treating medium in the range 1:1 to 1:5 by volume.

6. A process according to claim 1 in which the caustic wash is carried out using a 15-25% by wt. alcoholic alkali metal hydroxide solution at a ratio of hydrocarbon to treating medium in the range 2:1 to 1:2 by volume.

7. A process according to claim 1 in which the caustic wash is carried out using a reaction temperature in the range 60-100 C.

8. A process according to claim 1 in which the microorganism which is cultivated is a yeast.

9. A process according to claim 8 in which the yeast is of the family Cryptococcaceae.

10. A process according to claim 9 in which the yeast is of the sub-family Cryptococcoideae.

11. A process according to claim 10 in which the yeast is of the genus Torulopsis.

12. A process according to claim 9 in which the yeast is of the genus Candida.

13. A process according to claim 12 in which the yeast is Candida lipolytica.

14. A process according to claim 1 in which the microorganism is a bacteria.

References Cited by the Examiner UNITED STATES PATENTS 2,697,061 12/1954 Harris et al. -1 2,697,062 12/1954 Cramer 195-1 2,742,398 4/1956 Zo Bell 195-3 2,868,722 1/1959 Brooks et al 208-203 2,982,692 5/1961 McDill 195-3 2,988,500 6/1961 Gleim et a1 208-203 3,069,325 12/1962 Hitzman 195-2 3,152,068 10/ 1964 Price 208-203 OTHER REFERENCES Cook, The Chemistry and Biology of Yeasts, Academic Press Inc., New York, 1958, pp. 648659.

Wickerham et al., Carbon Assimilation Tests for the Classification of Yeasts, Journal of Bacteriology 56, 1948, pp. 363-371.

A. LOUIS MONACELL, Primary Examiner.

D. M. STEPHENS, Assistant Examiner. 

1. A PROCESS FOR THE REMOVAL, AT LEAST IN PART, OF WAXES FROM A WAX-CONTAINING PETROLEUM GAS OIL WHICH COMPRISES, IN A MIRCO-ORGANISM GROWTH STAGE, CULTIVATING A STRAIGHT CHAIN HYDROCARBON CONSUMING-MIRCO-ORGANISM IN THE PRESENCE OF SAID WAX-CONTAINING PETROLEUM GAS OIL; IN THE PRESENCE OF AN AQUEOUS NUTRIENT MEDIUM, AND IN THE PRESENCE OF GAS CONTAINING FREE OXYGEN, THEREAFTER SEPARATING THE MICRO-ORGANISM FROM THE GAS OIL OF REDUCED CONTENT OF WAS, AND SUBJECTING THE GAS OIL TO A CAUSTIC WASH TO EDUCE ITS CLOUD POINT. 